[Xen-devel] Empty struct in public headers Was: Re: [PATCH for Xen 4.5] xen/arm: Add support for GICv3 for domU

[Julien Grall <julien.grall@xxxxxxxxxx>]

(Rename the mail and strip the cc list)

On 11/18/2014 03:35 PM, Ian Jackson wrote:
> Julien Grall writes ("Re: [PATCH for Xen 4.5] xen/arm: Add support for GICv3 
> for domU"):
>> On 11/18/2014 03:10 PM, Ian Jackson wrote:
>>> Empty structs are a gcc extension (`(gcc-4.4) Empty Structures').  I
>>> would be very surprised if clang didn't support them too.
>>
>> AFAIK, clang doesn't complain about empty structures.
> 
> Right.
> 
>>> AIUI our policy, gcc extensions are fine except in the Xen public
>>> headers.
>>
>> We have at least 2 "empty" structure on the ARM public header.
> 
> That ought to be fixed, in case anyone ever wants to build ARM guests
> with Norcroft C or something.
> 
> Does the size of these structs matter ?

The 2 structures are arch_vcpu_info and arch_shared_info.

They are used only at the end of the structure vcpu_info (resp.
shared_info). So I guess we could fix it?

>> Would something like below be better?
>>
>> struct
>> {
>>   int dummy:1
>> };
> 
> I don't see why you wouldn't just do
>    struct blah { char dummy; };
> or even int dummy;

It was to avoid using more bit than necessary. I will use your solution.

Regards,

-- 
Julien Grall

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